EtherCAT-based high precision synchronous control expands TFT-LCD production capability

The manufacture of LCD and related display devices is widely expected to experience dramatic expansion in the near future. Global production of flat panel displays is conservatively forecast to treble or more by the end of the decade.

According to Chia-Wei Yang, Market Development Manager for ADLINK's Automation Business Center, adoption of biaxial synchronous gantry control can, however, address the problem, resolving the difficulty presented by uneven forces at the ends of the beam and eliminate the exceedingly large resulting error (> 10um), thereby supporting the requisite level of machine precision.

A leading supplier of visual inspection machines recognized the need for implementation of new-generation motion control. After researching available solutions, EtherCAT presented itself as the most effective means of securing necessary levels of synchronous control. Benefits included reduced noise interference and raised production output with superior bandwidth while slashing costs in a variety of areas, such as simplifying cabling. Additionally, full upgrade to the new system was expected to be surprisingly brief.

The display provider, in migrating from single gantry control to synchronous three-gantry operation, was able to take full advantage of synchronous control commands' latency of less than 1ms, which significantly boosted production efficiency and reduced deployment costs greatly. A comparatively short turnaround switching to the new system further added to the benefits accrued, altogether presenting an effective example of solution success.

Time and effort are, of course, required to effect the system upgrade, largely since the control program developed for the original architecture has to be scrapped and a new program created. In this case, fortunately, the provider's existing architecture control was based on ADLINK's MNET motion control cards and APS Function Library, comprising programs that are efficiently reusable. When the decision was made to switch to ADLINK's PCIe-8338 EtherCAT-based Motion Control Card, a complete program overhaul was not required, cutting the upgrade process down to a mere four weeks.

EtherCAT is able to boost production efficiency not only via the PCIe-8338's support for synchronous control of three gantries, but also a decentralized control design. In the case of legacy serial communication architectures such as MNET, a communication card has to work with an intermediary control module to control servo motors. Each control module can connect with four motors and control only the synchronous movement of the four motors. If a control module A controls motors 1 through 4 and a module B controls motors 5 through 8, motors 1 and 7 cannot form a gantry, since cross-module control is not supported.

EtherCAT eliminates this impediment, since no intermediary control module is required between master and slave. Any two of the eight motors, regardless of position, can form a gantry and synchronous motion of up to three sets (6 axes) is fully enabled.

By eliminating the control module and enabling 6-axis synchronous motion, the EtherCAT solution frees users from layout and mechanical limitations when developing control programs. Arbitrary selection and adjustment of targets for synchronous motion are fully supported, enabling advancement from sequential to continuous production and better ensuring uninterrupted flow from one station to the next. The provider in this case was, accordingly, able to achieve a 20% boost in production efficiency and an impressive 15%-30% cost reduction.

The EtherCAT control layer is designed with a simplified structure, thereby eliminating module costs. Furthermore, ADLINK's EtherCAT master always supports a wide range of slave devices. Users can freely choose from a variety of motors without being tied to specific brands, dramatically reducing costs while boosting production.